coal dust and its uses

1. - By Paarth Gupta

2.  COAL DUST IS A FINE POWDERED FORM OF COAL, WHICH IS CREATED BY THE
CRUSHING, GRINDING, OR PULVERIZING OF COAL. BECAUSE OF THE BRITTLE
NATURE OF COAL, COAL DUST CAN BE CREATED DURING MINING,
TRANSPORTATION, OR BY MECHANICALLY HANDLING COAL. IT IS A FORM
OF FUGITIVE DUST.
 GRINDING COAL TO DUST BEFORE COMBUSTING IT IMPROVES THE SPEED AND
EFFICIENCY OF BURNING AND MAKES THE COAL EASIER TO HANDLE. HOWEVER,
COAL DUST IS HAZARDOUS TO WORKERS IF IT IS SUSPENDED IN AIR OUTSIDE
THE CONTROLLED ENVIRONMENT OF GRINDING AND COMBUSTION EQUIPMENT.
IT POSES THE ACUTE HAZARD OF FORMING AN EXPLOSIVE MIXTURE IN AIR AND
THE CHRONIC HAZARD OF CAUSING PULMONARY ILLNESS IN PEOPLE WHO
INHALE EXCESSIVE QUANTITIES OF IT.
 THE DISTRIBUTION OF THE PARTICLE-SIZE OF COAL DUST IS FREQUENTLY
MEASURED IN MESH.

5.  COAL DUST ADDITIVATED WITH WATER SOLUBLE
CARBOHYDRATES FOR USE IN THE GREEN SAND
COMPOSITION FOR MOLDING OF CASTINGS REFERS TO A
PROCESS FOR OBTAINING COAL ADDITIVATED WITH
CARBOHYDRATES TO BE USED IN THE GREEN MOLDING
SAND COMPOSITION, COMMONLY USED FOR MAKING
CASTING MOLDS, HAVING AS A SCOPE TO INHIBIT THE
SAND SINTERING ON THE CASTINGS AND SO TO IMPROVE
THEIR FINISH.

6.  TO PREVENT SAND BURN ON AND THUS IMPART GOOD SURFACE FINISH TO THE
CASTING
 TO AID SEPARATION OF SAND AND CASTING AT KNOCK OUT
 TO LESSEN THE INCINDENCE OF EXPANSION DEFECTS SUCH AS: SCABBING.
 TO IMPROVE:-
A) PERMEABLIITY
B) SURFACE FINISH
C) MOULDABILITY
D) GREEN STRENGTH

7.  THE PROPORTION BY WEEIGHT OF THE COLD DUST REQUIRED IN
GREEN SAND MOULDING VARIES FROM 2 TO 3 % FOR VERY
SMALL CASTING.
 AND 7 TO 8 % FOR HEAVY WORK, ALTHOUGH HIGHER LEVELS
ARE SOMETIMES USED ION SPECIAL CASES.
 COLD DUST SHOULD BE WEIGHED OR METERED

8.  IF TOO MUCH COAL DUST IS ADDED TO THE MOULDING SAND,
THE CASTING MAY HAVE THE FOLLOWING DEFTCT:
 CRAZED SURFACES
 GAS HOLES
 ROUNED EDGES
 WHEN ANY OF THESE DEFECTS ENCOUNTERED THE ADVISIBILITY
OF THE REDUCING THE AMOUNT OF COAL DUST ADDED SHOULD
BE CONSIDERED. A DECREASE IN PERMEABILITY AND AN
INCREASE IN MOISTURE REQUIREMENT OF THE SAND BOTH
POINT TO EXCESS COAL DUST.

9. GAS HOLES

10.  COAL DUST SUSPENDED IN AIR IS EXPLOSIVE—COAL DUST HAS FAR
MORE SURFACE AREA PER UNIT WEIGHT THAN LUMPS OF COAL, AND IS MORE
SUSCEPTIBLE TO SPONTANEOUS COMBUSTION. AS A RESULT, A NEARLY EMPTY
COAL STORE IS A GREATER EXPLOSION RISK THAN A FULL ONE. THE
WORST MINING ACCIDENTS IN HISTORY HAVE BEEN CAUSED BY COAL DUST
EXPLOSIONS, SUCH AS THE DISASTER AT SENGHENYDD IN SOUTH WALES IN
1913 IN WHICH 439 MINERS DIED, THE COURRIÈRES MINE DISASTER IN
NORTHERN FRANCE WHICH KILLED 1,099 MINERS IN 1906, THE LUISENTHAL
MINE DISASTER IN GERMANY, WHICH CLAIMED 299 LIVES IN 1962, AND THE
WORST: THE EXPLOSION AT BENXIHU COLLIERY, CHINA, WHICH KILLED 1,549 IN
1942. SUCH ACCIDENTS WERE USUALLY INITIATED BY FIREDAMP IGNITIONS,
THE SHOCK WAVE OF WHICH RAISED COAL DUST FROM THE FLOOR OF THE
MINE GALLERIES TO MAKE AN EXPLOSIVE MIXTURE. THE MAIN ATTEMPTS AT
PREVENTION INCLUDE USING SAFETY LAMPS, ADDING STONE DUST COFFERS
TO MINE GALLERIES TO DILUTE THE COAL DUST, WATERING WORKINGS AND
ENSURING EFFICIENT VENTILATION OF ALL THE WORKINGS.